1. Field of the Invention
The present invention relates to an electrophotographic copying machine equipped with a document-detecting device that detects the density and the size of a document to be copied.
2. Description of the Prior Art
In an electrophotographic copying machine, documents with various densities and sizes are used for copying. On the conventional electrophotographic copying machine, therefore, an image density control device is provided so that the best copied image can be obtained even for the document with various density and various size and a user controls densities manually counting on his experience according to the density of the document. As for the size, on the other hand, the recording paper corresponding to the size of a document is selected by checking the size mark indicated on the cassette and the like of the mark indicated on the panel. However, such manual density adjustment is troublesome in operation and therefore, there has been proposed a copying machine wherein the density and the size of a document are automatically detected before copying and an image density is automatically controlled and a feeding paper size is automatically selected.
In the past, there has been known a method to control the density conditions from the maximum value and the minimum value of the density as a method to detect the density of a document and to control automatically an image density, as proposed by Japanese Patent Publication Laid-Open to Public Inspection No. 93834/1978, but there has been a drawback that density conditions are controlled from the rule marks alone for the document having images darker than the density of the most necessary image such as a pencil-written document with rule marks. Accordingly, like the case of Japanese Patent Publication Laid-Open to Public Inspection No. 120623/1980, there has been proposed a method to scan the document placed on the document table to make a histogram according to the density distribution of various points of the document and to adjust to the predetermined image density according to the pattern of the histogram, but the circuit structure to make the histogram is inevitably complicated.
As a conventional document size-detecting method, on the other hand, there has been known a method wherein plural sensors are arranged at fixed positions on the platen cover and a document size is detected by the output signals from such sensors, absolutely separately from the method to detect the density of the document. This method has a problem that the structure of the platen cover is complicated, which causes an increase in cost.